An image-forming optical field carries both amplitude and phase information. However, conventional imaging systems record only the amplitude information and the phase information is lost. This limits the capability and the range of applications of conventional imaging technologies.
Conventional imaging systems do not fully utilize the unscattered transmitted or reflected light for the noiseless amplification of the weak image-forming field. This makes conventional imaging systems unsuitable for some tasks.
Phase-contrast microscopes perform a phase-to-intensity conversion to render phase objects visible. However, they can determine neither the phase nor the true amplitude of the image-forming field. Interferometers can determine both the phase and the amplitude of an optical field. However, conventional interferometers do not provide high enough spatial resolution to be used for imaging.
Some special interferometers such as the Linnik interferometer can determine both the phase and the amplitude with high spatial resolution and therefore can in principle be used for imaging. However, they are unstable because the probe beam and reference beam take separate paths to the image sensor.
The following references set forth techniques for extending phase-contrast microscopy and use a phase-stepping method to extract phase information of the sample: A. Y. M. Ng, C. W. See & M. G. Somekh “Quantitative optical microscope with enhanced resolution using a pixilated liquid crystal spatial light modulator” Journal of Microscopy, Vol. 214, Pt 3 June 2004, pp. 334-340, Gabriel Popescu, Lauren P. Deflores, Joshua C. Vaughan, et al “Fourier phase microscopy for investigation of biological structures and dynamics”, U.S. Pat. No. 7,365,858 and U.S. Application Publication No. 2005/0105097 A1. However, these references do not show how to extract both phase and amplitude information from the measured image data, thus limiting their capability and applications.
International Patent Application Publication No. WO 2009/149103 A1, entitled “Interferometric Defect Detection and Classification,” describes apparatuses and methods for defect detection and classification using a high-resolution common-path interferometric imaging system. However, it does not explicitly show how the apparatus can be used for imaging. In particular, it does not show how to remove the effects of aberrations and how to achieve a higher spatial resolution than conventional imaging techniques.